Most UK loco designers seem to have tried to keep the cylinders horizontal and the centre line of them close to the centre line of the axles. There were exceptions such as the LMS "Crabs", but that was unusual enough for the design to have acquired the nickname because of the different appearence.

Churchward on the GWR kept his cylinders horizontal but allowed them to be 2.5" higher than the centre line in order to get sufficient outside clearance on the "loading gauge", that is the outline profile that all the stock on the line had to fit inside. UK loading gauge is much more restricted than USA, and I think USSR was even bigger.

Also bear in mind that the "stroke" (length that the piston moves through) of the cylinder has an effect, the radius of the circle that the connecting rod describes where it is attached to the wheel is half the length of the stroke and coupled with the diameter of the wheel this can give a very different visual effect for different locos. Later UK express locos tended to have driving wheels about 6' 6" to 6'9", but in the days of the single drivers 7' and 8' were more common. The Bristol and Exeter even had some 4-2-4T express tank locos with 9' wheels with no flanges, no coupling rods or connecting rods on view either!

Another thing to influence the appearance is the type of valve gear fitted and whether it is outside on view or hidden inside.

Robin